Experts said this finding could help them pack more phenolic compounds into broccoli in the future, to make it even healthier.

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Jack Juvik, a geneticist from University of Illinois, said: "Phenolic compounds have good antioxidant activity, and there is increasing evidence that this antioxidant activity affects biochemical pathways affiliated with inflammation in mammals.

"We need inflammation because it’s a response to disease or damage, but it’s also associated with initiation of a number of degenerative diseases.

"People whose diets consist of a certain level of these compounds will have a lesser risk of contracting these diseases."

Researchers crossed two broccoli lines and analysed their total phenolic content as well as their ability to neutralise oxygen radicals.

They then used a genetic technique called "quantitative trait locus analysis" to search for the genes involved in generating phenolics in the most promising broccoli species.

By identifying the genes involved in accumulating these compounds, researchers believe they are one step closer to breeding broccoli, and other Brassica vegetables like kale and cabbage, with mega-doses of phenolic compounds.